A VERY RARE COMBINATION
Only about 1 to 2 percent of the world’s population has natural red hair. But red hair isn’t the only thing that makes them unique; it’s just the most noticeable of their genetic differences.
People with red hair produce a lot of pheomelanin and less eumelanin, which are two types of melanin that determine whether hair is red or brown. Melanocytes, the cells that produce melanin, have a protein called the melanocortin 1 receptor, or MC1R.
Normally, this protein causes melanocytes to make more eumelanin than pheomelanin. However, redheads have a genetic variant that makes MC1R work the opposite way, leading to less eumelanin and more pheomelanin. These genetic variants are recessive, meaning that to be born with red hair, either the parents do not have red hair but carry the gene (25%), one parent has red hair and the other is a carrier (50%), or both parents have red hair (almost 100%).
Most people with red hair, like everyone else, have brown, hazel, or green eyes. Having both red hair and blue eyes is very rare because both traits are recessive. This means both parents must have the right genes for their child to have both features. Red hair naturally occurs in 1-2% of the human population, increasing to 2-6% in the northern hemisphere, while 17% of the world’s population has blue eyes.
So, only about 0.2% of the population has both red hair and blue eyes.
Sources: “ARE REDHEADS WITH BLUE EYES REALLY GOING EXTINCT?”, University of Melbourne; “Red for danger: the effects of red hair in surgical practice”, bmj